A smart grid means the next generation intelligent power grid through which a power supplier and a consumer bi-directionally exchange real time information with each other using a state-of-the-art information communication technology (ICT) to optimize energy efficiency. That is, it is to raise efficiency, reliability, and stability of a power grid and efficiently manage distributed resources through innovation of generating, supplying, and using systems of energy utilizing the power network and the state-of-the-art ICT (bidirectional communication, sensors, computing, and software).
In addition, a green power information technology (IT) means a technology of freely creating and distributing various power information by installing power plants, power-transmission towers, electric poles, and a number of sensors in electric home appliances. A traditional power supplying system that has been used up to now is subjected to power transmitting and distributing processes of converting a large capacity of electricity generated by a power generating company into high voltage, middle voltage, and low voltage electricity, and has a power company-centric unilateral structure (centralized power supplying structure) in which a balance of production (power generation) and consumption (demand) of power is provided by controlling a power generation sector.
However, since the traditional power supplying system as described above uses physical switches or analog type controllers, it has a limitation in long distance power transmission or power transmission and distribution between regional power companies, control and adjustment of various distribution power supplies such as wind force, sunlight, or the like, necessity to control a power demand section for securing reliability and safety of power, and the like. Therefore, a horizontal, cooperative, distributed, and flexible power network has been demanded, such that smartness of a power grid starting with grafting a computer and a communication technology into an existing power distribution network has been spread to all fields such as power transmission, power transformation, demand management, and the like.
Here, an energy storage system (ESS) is a requisite component of the smart grid, and it is necessary to apply an energy storage technology in order to stabilize intermittent output characteristics of a renewable power generation source such as sunlight, wind force, or the like, in the short term and overcome a time difference between power generation and a demand.
However, since energy storage systems according to the related art have a defined capacity, in the case in which a capacity of the energy storage system should be increased due to an increase in a load amount, a new energy storage system corresponding to a total required capacity should be installed.
In addition, although a separate battery is connected to an existing energy storage system having a small capacity to increase a capacity of the energy storage system, the energy storage system and a power line of the separate battery should be directly connected to each other, which is difficult and troublesome.
As the related art, U.S. Patent Application Publication No. 2012-0181956 entitled “Device for Storing Electrical Energy” has been disclosed.